1. Field of the Invention
The present invention is directed to a flow-through measurement cell for the extracorporeal measurement of blood parameters, of the type having a pressure sensor arranged in a measurement chamber.
2. Description of the Prior Art
A flow-through measurement cell of the general type described above is known from PCT publication WO 92/05449. This flow-through measurement cell has a first measurement chamber with several electrochemical sensors arranged therein. An inlet opening of the first measurement chamber is connected with a switching unit via a liquid connection line. A liquid conveyor apparatus is connected to an outlet opening of the first measurement chamber. Dependent on the switch position of the switching unit, liquid being measured, rinse solution or calibration solution can be suctioned through the measurement chamber by means of the liquid conveyor apparatus and then conveyed into a waste receptacle. Separately from the first measurement chamber, a pressure sensor is arranged in a second measurement chamber of the flow-through measurement cell. The second measurement chamber is connected with the switching unit via an additional liquid connection line. In the switching unit, in the switching states "ready" and "measure" a connection is created to a measurement line, so that in these switch positions a continuous pressure measurement can ensue.
An additional flow-through measurement cell for extra-corporeal measurement of several electrochemically measured blood parameters, such as e.g. pH concentration, pO.sup.2 concentration, pCO.sub.2 value and electrolyte concentration, is described in U.S. Pat. No. 4,841,974. It is connected to an arterial permanent catheter. The sensors are arranged in the flow-through measurement cell in a wall of a measurement duct. The sensors themselves are fashioned as ion-sensitive field-effect transistors that are jointly integrated on a silicon chip. A membrane, which forms a boundary surface to the measurement medium, i.e. to the removed blood, thereby serves as a control electrode. An allocated evaluation electronics is likewise integrated on the chip, and forms a structural unit with the sensors. The construction of the chip is also specified in the article by W. Gumbrecht, D. Peters, W. Schelter, W. Erhardt, J. Henkel, J. Steil and U. Sykora: "Integrated pO.sup.2, pCO.sub.2, pH Sensor System for Online Blood Monitoring," Sensors and Actuators B, 18-19 (1994), pp. 704-708.
In European Application 0 714 017, silicon thin film pressure sensors are specified that can be manufactured in a manner compatible with processes that are standard in CMOS technology. As used herein, "compatible with CMOS manufacturing processes" means that the additional process steps required in the manufacture of the sensor can be incorporated into standard CMOS process steps, and do not disturb them. This technology is also known as surface micromechanics technology. In addition to the pressure sensor, further electronic circuits are monolithically integrated on the same chip.
In a different type of technology also used for surface micromechanics, known as bulk micromechanics technology, the sensors are etched considerably deeper into the silicon substrate material than in the surface micromechanics technology.